c# - How to convert stream to bitmap in xamarin.forms to adjust image contrast

Question

I am trying to raise the contrast of an image in Xamarin.forms using this algorithm. My code gives me in image in the form of a System.IO.Stream, which I want to convert to a Bitmap/LockBitmap to use the algorithm.

I tried code such as using System.Drawing, which didn't work. The error said "the type or namespace bitmap could not be found." Then, I tried using Android.Graphics, which fixes that error, but I don't know if it will work with a Xamarin.forms app that needs to run on Android and iOS.

Even if that does work, how do I actually convert a System.IO.Stream into a Bitmap? Is there another algorithm that doesn't require bitmaps?

Edit: I think I can use BitmapFactory to convert the stream into a bitmap.

Answer 1

you could use DependencyService to convert System.IO.Stream into Bitmap ,after raise the contrast of an image ,return the new stream,and show the Image in forms page.

like:

create a interface IRaiseImage.cs:

public interface IRaiseImage
{
    Stream RaiseImage(Stream stream);
}

then in Droid.project,creat AndroidRaiseImage.cs:

[assembly: Dependency(typeof(AndroidRaiseImage))]
namespace App18.Droid
{
  class AndroidRaiseImage : IRaiseImage
   {
     public Stream RaiseImage(Stream stream)
      {
        Bitmap bitmap = BitmapFactory.DecodeStream(stream);
        //raise the bitmap contrast
        ...
        // return the new stream
        MemoryStream ms = new MemoryStream();
        bitmap.Compress(Bitmap.CompressFormat.Png, 100, ms);
        return ms;
      }
   }
}

then you could set to the Image in your forms page:

MemoryStream memoryStream = new MemoryStream();//your original image stream
Image image = new Image();
image.Source = ImageSource.FromStream(() => DependencyService.Get<IRaiseImage>().RaiseImage(memoryStream));